“It happens more than you would think,” said Dr. Kimberly Gecsi, who works at University Hospitals Case Medical Center in Cleveland.

“Every time it does there’s always the, ‘How could they not have known? It seems crazy.’”

Gecsi gets two or three cases of this type on average every year, she said. It occurs mostly among young women, who she said are in denial.

“Teenagers will until the day they die say I don’t have sex, so it just doesn’t occur to people,” she said.

But sometimes even doctors miss the seemingly obvious.

“I’ve had patients sent to me by family practitioners convinced the patient had cancer,” Gecsi said.

Though babies born to unprepared mothers are often born healthy — as the Michigan baby was last week — missed prenatal care isn’t a good thing, said Dr. Jennifer Ashton, a senior medical contributor for ABC News who has a private OB-GYN in New Jersey.

Her advice to women of child-bearing age: “Be familiar with your own body and pay attention to the way in which it talks to you. Prenatal care is really important for not just the baby but the mother also,” said Ashton, an OB-GYN at University Hospitals Case Medical Center.

Last Friday morning, Linda Ackley arrived at the hospital, Allegiance Health, for a CT scan to check the supposed hernia. She said she had a “bloated abdomen” a week earlier.

An initial scan revealed she was pregnant. Doctors told Ackley she would deliver in three to four weeks. But a second scan taken soon after showed that she had carried the baby to full term, 40 weeks.

So hospital staff wheeled Ackley in for an emergency delivery. The baby was born Friday night.

The surprise birth follows a medical scare in 2011 for the Ackleys, high school sweethearts who had been married for 24 years. Linda Ackley contracted necrotizing fasciitis, a bacterial infection that attacks soft tissue. After spending a week in a coma, doctors had to remove some of her stomach muscles.

She had been told she might not live. Now looking back, she views the illness in a new light.